Packaging containers commercially available on the market which are under continuous inner excess pressure because they are filled with a pressurised liquid food such as beer, carbonated soft drinks, carbonated water or sparkling wine today consist of containers produced from glass, plastic or metal.
Attempts have been made to manufacture such containers from a packaging laminate comprising core layers of paper and paperboard, as well as gas barrier layers and liquid barrier layers. However, in such contexts one problem occurs which may be traced to the stretching or straining of the fibres in the paper or paperboard layer (the core layer). The reason for this is that, on the production of the paper or paperboard layer in a paper or paperboard machine, the fibre network is stretched in the machine direction of the paper or paperboard machine, while a corresponding stretching in the transverse direction does not take place. Further, the fibres are substantially oriented in the machine direction of the paper or paperboard web as a result of the forming of the web when a stock jet of a cellulose stock is directed at the wire which runs in the machine direction.
When a tubular packaging container for a pressurised, liquid food is to be produced from a packaging laminate which includes a core layer of such paper or paperboard, the paper or paperboard is suitably utilised such that the machine direction of the paper or paperboard coincides with a tangent to the circumference of the packaging container, i.e. the paper or paperboard is disposed such that the fibres are principally oriented in a direction around the circular circumference of the container. The reason for this is that the paper or paperboard displays the greatest strength in this direction, because of the fibre orientation, at the same time as the greatest strains in the material, because of the inner excess pressure, occur in this direction. However, strains will naturally also occur as a result of the inner excess pressure in the axial direction of the container, which implies that the paper or paperboard material will expand (“creep”) in the axial direction of the container so that the container increases in length after having stood for some time on the shelf. This is particularly because the fibres initially, as per the above, do not display an appreciable stretching in the transverse direction of the paper or paperboard, i.e. in the axial direction of the container. If, instead, the packaging laminate were to be turned through 90°, this problem would naturally instead occur in the tangential direction of the container, in which event the container would swell and there would at the same time be a risk of failure.
WO 99/59882 discloses a packaging laminate which is formed with several, e.g. four, layers of paper or paperboard. Moreover, the risk of failure has been reduced in that the longitudinal joints for these different layers have been disposed in different positions around the circumference of the container. This formation of the packaging laminate and container is not, however, commercially viable because of the extreme costs which are incurred because of the large thickness—or in other words the large quantity—of paperboard which is consumed and because of the complex process for realising longitudinal joints in different positions around the circumference of the container.